Hydrogenation of aromatic hydrocarbons

ABSTRACT

AROMATIC HYDROCARBON FEEDSTOCKS CONTAINING ORGANIC SULFUR COMPOUNDS ARE HYDROGENATED IN A &#34;SINGLE-STAGE&#34; PROCESS, UTILIZING A DUAL-CATALYST HYDROGENATION SYSTEM. THE FEED IS FIRST HYDROFINED OVER A SULFACTIVE CATALYST SELECTIVE FOR THE HYDROECOMPOSITION OF ORGANIC SULFUR COMPOUNDS, AND TOTAL EFFLUENT IS THEN HYDROGENATED OVER A SULFUR-SENSITIVE GROUP VII NOBLE METAL HYDROGENATION CATALYST ACTIVE FOR THE HYDROGENATION OF AROMATIC HYDROCARBONS.

United States Patent Office 3,691,060 HYDROGENATION OF AROMATIC'HYDROCARBONS Texas V. Inwood, 1932 Fullerton Road, La Habra, Calif.90631 No Drawing. Continuation-impart of application Ser. No. 796,895,Feb. 5, 1969, now Patent No. 3,592,758. This application Mar. 24, 1971,Sera No. 127,749

Int. Cl. Cg 23/04 U.S. Cl. 208-89 16 Claims ABSTRACT OF THE DISCLOSURERELATED APPLICATIONS This application is a continuation-in-part of Ser.No. 796,895, filed Feb. 5, 1969, now US. Pat. No. 3,592,758.

BACKGROUND AND SUMMARY OF INVENTION It is well known that Group VIIInoble metal catalysts, e.g., platinum-alumina, are very active for thehydrogenation of aromatic hydrocarbons, but that their activity iseasily poisoned by sulfur compounds. When it is desired to hydrogenatesulfur-containing feedstocks over Group VIII noble metal catalysts, ithas therefore become conventional procedure to pretreat such feeds forsulfur removal. The most commonly employed pretreatment is catalytichydrofining, wherein the feed is subjected to hydrogenating conditionsin the presence of a sulfactive hydrofining catalyst such ascobalt-molybdenum-alumina compositions, whereby the organic sulfur isconverted to hydrogen sulfide. These hydrofining catalysts displayrelatively poor activity for the hydrogenation of aromatic hydrocarbons,especially monocyclic aromatics.

It has generally been assumed, when hydrogenating sulfur-containingfeeds, that the active poisoning agent for the noble metal hydrogenationcatalysts consists mainly of hydrogen sulfide, which is generated underhydrogenating conditions from the organic sulfur compounds in the feed.It has been hypothesized that the hydrogen sulfide converts at least thesurface of the noble metal to sulfided species which are less active forthe hydrogenation of aromatic hydrocarbons. Under this hypothesis, itmight be assumed that organic sulfur compounds which combine lessreadily with the noble metal, and which are relatively ditficultlydecomposed under hydrogenating conditions, e.g., thiophene, would exerta lesser poisoning elfect than would hydrogen sulfide, or other sulfurcompounds which are easily decomposable to hydrogen sulfide. I have nowdiscovered that these hypotheses appear to be incorrect, and that themore refractory organic sulfur compounds exhibit a greater deactivatingeifect on noble metal catalysts than does hydrogen sulfide or easilydecomposable organic sulfur compounds. This discovery has led to thepresent invention, which effects a considerable economy in thehydrogenation of certain aromatic feedstocks which contain moderateamounts of organic sulfur compounds.

Under the previous hypothesis that hydrogen sulfide was the most potentof the sulfurous catalyst poisons, it was considered mandatory in allcases where a feedstock con- Patented Sept. 12, 1972 tained sufiicientorganic sulfur to require prehydrofining, to remove the hydrogen sulfidegenerated during hydrofining prior to contacting the purified feedstockwith the noble metal catalyst. This has always resulted in a fulltwo-stage process, with intervening cooling and condensation of thehydrofiner efiiuent, recycle of separated hydrogen to the hydrofiner,caustic and/ or water-washing of the condensate, and reheating of thewashed condensate feed to the hydrogenation zone, for which a separatehydrogen recycle system must be maintained. The need for two separateheat exchangers for product condensation, two separate recycle gascompressors, as well as the interstage washing facilities, and theattendant increased utility requirements, adds greatly to the expense ofsuch a twostage system, as compared to a single-stage system involvingthe same total catalyst volume.

Moreover, the two-stage system in all cases requires two separatereactors, whereas in a single stage process it is often more economicalto employ a single reactor enclosing both the hydrofining and thehydrogenation catalyst beds. In my process, the hydrofining andhydrogenation catalysts may be disposed in the same reactor or separatereactors as desired (an economic factor which depends mainly on plantsize), and the entire process can be operated with a single heatexchange system for product condensation, and with a single recycle gassystem. These economies are found in many cases to far offset the costof the slightly larger volume of hydrogenation catalyst required tocompensate for the poisoning effect of the hydrogen sulfide which isallowed to pass therethrough.

From the foregoing, it will be apparent that my unexpected discovery ofthe difierence in poisoning effect as between H 8 and organic sulfurenables the refiner to eifect substantial economies in the hydrogenationof a certain class of feedstocks, i.e., those feeds which containsufficient sulfur to warrant a prehydrofining step, but insufficient towarrant the expense of a full two-stage process. Obviously, for feedscontaining very minimal amounts of sulfur, it may be economicallypreferable to increase the size of the hydrogenator slightly anddispense entirely with the prehydrofiner. And in the case of feedscontaining very large amounts of sulfur, two-staging the process forintervening H 8 removal may be desirable because the required capitaland utility expenses would be less than the incremental costs of themuch larger hydrogenation reactor and catalyst volumes required tomaintain conversion at very high H S levels.

However, it is within the scope of my invention to practice the presentsingle-stage process even with feedstocks which under present economicconditions could be more economically processed without prehydrofining,or in the conventional two-stage system. Although, under presenteconomic conditions, my process is particularly economical for thehydrogenation of feedstocks containing between about 5 and 500 ppm. oforganic sulfur in the form of 0 compounds, these values could changedrastically with advancing technology, as for example the discovery ofmore efficient hydrofining catalysts (which might reduce the 5 ppm.figure to 1 ppm. for example), or the discovery of cheaper and moreelfective noble metal hydrogenation catalysts (which might raise the 500ppm. figure to 5,000 ppm. for example). With any feedstock containingundesirable amounts of sulfur, there is some advantage to be gained inthe utilization of my dual-catalyst, single-stage system, as compared tothe noble metal single-catalyst system, where under prior art premisesno such advantage would be expected.

Surprisingly, I have found that the organic sulfur compounds which exertthe strongest poisoning effect upon the noble metal hydrogenationcatalysts are those which are incapable of chemically combining with thebulk noble metal, i.e., organic sulfides, and particularly cyclicsulfides such as thiophene. Mercaptans appear to be intermediate intheir poisoning effect between hydrogen sulfide and organic sulfides,although the lower mercaptans, methyl and ethyl mercaptan, aresubstantially equivalent to hydrogen sulfide in this respect. The termsulfide is employed herein to designate any sulfhydrocarbon containingsulfur bonded exclusively to carbon atoms. My invention is particularlyadvantageous for the hydrogenation of feedstocks containing sulfidesulfur in amounts ranging between about and 300 p.p.m.

DETAILED DESCRIPTION (A) Feedstocks Feedstocks contemplated hereininclude any desired aromatic hydrocarbon or mixtures thereof, includingbenzene, toluene, xylenes, naphthalene, gasoline, solvent naphthas,kerosene, turbine fuels, diesel fuels, gas oils, catalytic crackingcycle oils, lubricating oils, or any desired fraction of such products.The aromatic content will ordinarily, though not necessarily, be greaterthan about volume-percent, and it is further preferred that the feedcontain at least about 5 volume-percent of monocyclic aromatichydrocarbons. As indicated above, the process is of greatest advantagein connection with feedstocks containing between about 5 and 300 p.p.m.(preferably between 10 and 150 p.p.m.) of sulfide sulfur. Nitrogencontent of the feed should preferably be below about 10 p.p.m. Thefeedstock may be derived from any desired source, e.g., petroleum crudeoils, shale oils, tar sand oils, coal hydrogenation products and thelike.

(B) Hydrofining conditions and catalysts The hydrofining conditions andcatalysts for the first stage of my process may be substantiallyconventional. Suitable catalysts may comprise any of the oxides and/ orsulfides of the transitional metals, and especially an oxide or sulfideof a Group VIII metal (particularly cobalt or nickel) mixed with anoxide or sulfide of a Group VI-B metal (preferably molybdenum and/ortungsten). Such catalysts are preferably supported on an adsorbentcarrier in proportions ranging between about 2 percent and 25 percent byweight. Suitable carriers include in general the difi'icultly reducibleinorganic oxides, e.g., alumina, silica, zirconia, titania, clays suchas bauxite, bentonite, etc. Preferably the carrier should display littleor no cracking activity, and hence highly acidic carriers having a Cat-Acracking index of above about 25 should be avoided. The preferredcarrier is activated alumina, and especially acvated alumina containingabout 3-15 percent by weight of coprecipitated silica gel.

The preferred hydrofining catalyst consists of a sulfided composite ofnickel and molybdenum supported on silicastabilized alumina.Compositions containing between about 1 percent and 8 percent of Ni, 3percent and 25 percent of Mo, 3 percent and percent of SiO, and thebalance alumina, and wherein the atomic ratio of Ni/Mo is between about0.2 and 4 are especially preferred.

Suitable hydrofining conditions may be summarized as follows:

HYDROFININ G CONDITIONS Operative Preferred Average bed temperature, F550-850 650-800 Pressure, p.s.1.g 150-3, 500 400-1, 500 LHs vm, 0. 2:200. 5-5 112/011 ratio, Mscf/b 0. 5-20 2-12 (C) Hydrogenation conditionsand catalysts Hydrogenation in the second stage of my process maylikewise be carried out under substantially conventional conditions,using conventional noble metal catalysts. The preferred metals areplatinum and palladium, but rhodium, ruthenium, iridium and osmium maybe used to less advantage. Mixtures of any two or more of such metalsare also contemplated. The metal or metals are preferably supported, asby impregnation, on an adsorbent, refractory oxide carrier which may be,but is not necessarily, of the same nature as described above inconnection with hydrofining catalysts. The proportion of noble metalnormally ranges between about 0.1 and 3 percent, preferably between 0.2and 1.5 percent by weight. Preferred catalysts comprise about 0.2-1percent by weight of platinum or palladium supported on activated gammaalumina, or eta alumina. Platinum-alumina catalysts conventionally usedfor the reforming of naphtha fractions may also be utilized.

The hydrogenation may be carried out under conditions summarizedgenerally as follows:

HYDRO GENAIION CONDITIONS As will be understood by those skilled in theart, the above conditions should be selected and correlated with thecatalyst and the feed to achieve the desired degree of hydrogenation.Normally it is desired to effect at least about percent hydrogenation ofthe aromatic hydrocarbons, but in many cases, as in the case of jetfuels and diesel fuels, a lesser degree of hydrogenation may be desiredin order to minimize hydrogen consumption.

It is also necessary to adjust and correlate the hydrogenationconditions (principally temperature) with the cracking activity of thecatalyst base in order to avoid undesired hydrocracking of the feed.Normally, it is desirable to avoid reducing the average molecular weightof the feed by more than about 5 percent, as measured on G product vs. Cfeed. The more conventional catalyst bases such as alumina, or aluminacogelled with about 1-15 of silica, have Cat-A cracking activity indexesup to about 25. When using this type of catalyst base, tempertaures inthe high ranges disclosed above, e.g., 450750 F. are normally preferred.

However, it has recently been found that the hydrogenation activity ofGroup VIII noble metal catalysts is markedly enhanced when such metalsare supported on more acidic supports having a cracking activity higherthan that corresponding to a Cat-A index of 25. As a result, when usingsuch catalysts, temperatures can be reduced to the lower ranges of e.g.,BOO-550 'F., while still achieving the desired hydrogenation of aromatichydrocarbons with less than 5 percent reduction in average molecularweight of the feedstock. Suitable acidic supports of this nature includefor example a composite of about 20 weight-percent of an SiO -15% Al Ocogel dispersed in 80 weight-percent of a low bulk density (0.4 ml./g.)alumina, the composite having a Cat-A cracking activity index of about40. Another exemplary acidic support consists of about 20 weight-percentof a stabilized hydrogen Y zeolite dispersed in alumina gel, thecomposite having a Cat-A activity index of about 65.

The efiluent from the hydrogenation zone is cooled and condensed at,e.g., 50-200 F. to recover the hydrogenated liquid product and ahydrogen-rich recycle gas which is normally recycled to the hydrofiningzone, although a portion thereof may be recycled to the hydrogenationzone if desired. Fresh makeup hydrogen may be supplied to either or bothstages of the process. In the case of high-sulfur feedstocks, it may bedesirable to scrub all or a portion of the recycle gas with caustic orgirbitol solvent to remove H 5, and thus present its buildup in thesystem.

(B) Process modifications While it is essential to the practice of myinvention that at least some of the hydrogen sulfide and hydrocarboneflluent from the hydrofining stage be passed through the hydrogenationzone, it is not essential that the entire hydrofiner effluent be sotreated. In some cases, as e.g., in the treatment of heavy feedstocks,the hydrofiner effluent may comprise a liquid phase and a vapor phase,and it may be desired to withdraw a portion of the liquid phase forother uses. Also, in the case of very high sulfur feedstocks, it may bedesirable to remove a portion of the hydrogen sulfide generated in thehydrofiner, as by oil absorption, or adsorption on solid adsorbents, orby other methods not requiring a full two-staging of the process. Theessential feature of my invention simply involves maintaining asingle-stage operation, with at least a substantial portion of thehydrogen sulfide and hydrocarbon effluent from the hydrofiner pasingthrough the hydrogenation zone.

In one contemplated modification, instead of a'single hydrofiner, twoseparate hydrofiners may be employed in alternating sequence in order toprovide for continuous operation where the hydrofining catalyst requiresregeneration more frequently than the hydrogenation catalyst. Othermodifications will be apparent to those skilled in the art.

The following examples are cited to illustrate the invention morespecifically, but are not to be construed as limiting in scope:

EXAMPLE I A previously hydrofined naphtha reformer feedstock washydrogenated at 550 F., 600 p.s.i.g., 8.0 LHSV with 4000 s.c.f. ofhydrogen per barrel of feed, over a commercial reforming catalystconsisting of 0.5 weight-percent Pt supported on a mixed eta-gammaalumina carrier in the form of extrudate. The principal feedstockcharacteristics were:

The ethyl mercaptan was added to simulate the effect of an equivalentamount of H 8 carried over from the hydrofiner, the lower mercaptanshaving previously been found to be substantially equivalent to H 8 intheir poisoning effect on Pt-Al O catalysts. The hydrogenated productwas found to contain 0.3 volume percent aromatics, corresponding to 98%converison. The first order reaction rate constant, based on theequation:

(where A is the aromatic content of the feed and A the aromatic contentof the product) was calculated to be 30.5.

EXAMPLE II Another naphtha feedstock which had not been prehydrofined,and which contained organic sulfides and mercaptans mainly in the C -Crange, was hydrogenated over the same catalyst and under the sameconditions as in Example I. The feed characteristics were as follows:

The hydrogenated product was found to contain 2.8 volume-percentaromatics, corresponding to only 92% conversion. The first order rateconstant was calculated to be 20.4. Thus, about 50% more catalyst isrequired to obtain the same conversion of the feed of this example thanfor the feed of Example I. To rule out the possibility that thisdifference might be due entirely to the slightly higher boiling range ofthis feed, or its slightly higher total sulfur content, the followingexperiments were carried out:

EXAMPLE III The feed of Example I was doped with ethyl mercaptan to atotal sulfur content of 23 p.p.m., and hydrogenated over the samecatalyst at 500 F., 600 p.s.i.g., 8.0 LHSV and 4000 s.c.f. H /B. Over113 hours of operation, the product aromatic content averaged 1.3volume-percent, corresponding to 90.5% conversion. The first order rateconstant was calculated to be 18.5.

EXAMPLE IV The feed of Example I was doped with 3-methylthiophone to atotal sulfur content of 26 p.p.m., and hydrogenated over the samecatalyst and under the same c0nditions as in Example III. The productaromatic content was 7.6 volume-percent, corresponding to only 43%conversion. The first order rate constant was calculated to be 4.57.Thus, over four times more catalyst is required to obtain the sameconversion of the thiophene-doped feed of this example than would berequired for the ethyl mercaptan-doped feed of Example III, even thoughthe overall sulfur content of the two feeds is substantially the same.It is thus clear that by prehydrofining a feed containing organicsulfides to convert the same to hydrogen sulfide, the resulting totaleffluent can be hydrogenated over noble metal catalysts much moreefliciently than could the raw feed.

In the foregoing examples, the hydrogenation catalyst employed was basedon a carrier having a Cat-A cracking activity index below 25, and thetemperatures were such that there was less than 5 percent reduction inaverage molecular weight of the feeds. Substantially the same resultsare obtained at hydrogenation temperatures 20- 40 F. lower than thoserecited in the examples when a catalyst is utilized comprising 0.5% Ptsupported on a composite base having a Cat-A cracking activity index of40, and comprising 20 weight-percent of an 85% SiO 15% A1 0 cogeldispersed in of alumina, in the form of a 1 extrudate having a bulkdensity of 0.5 gm./ml.

It is not intended that the invention should be limited to the detailsdescribed above, since many variations may be made by those skilled inthe art without departing from the scope or spirit of the followingclaims.

I claim:

1. A process for the hydrogenation of aromatic hydrocarbons in ahydrocarbon feedstock contaminated with organic sulfur compounds, whichcomprises:

(1) subjecting said feedstock plus added hydrogen to catalytichydrofining at an elevated temperature and pressure in contact with asulfactive hydrofining catalyst comprising a Group VI-B metal or sulfidethereof, to effect hydro-decomposition of at least a portion of saidorganic sulfur compounds with resultant product of hydrogen sulfide;

(2) subjecting effluent from step (1), comprising hydrogen, hydrogensulfide and hydrocarbon feedstock, to catalytic hydrogenation in contactwith a sulfur-sensitive catalyst comprising a Group VIII noble metalsupported on an adsorbent, refractory oxide carrier, said hydrogenationbeing carried out at a temperature correlated with the cracking activityof said carrier so as to effect hydrogenation of aromatic hydrocarbonsin said feedstock with less than about percent reduction in averagemolecular weight of the feedstock by hydrocracking;

(3) separating effluent from step (2) into a hydrogenated hydrocarbonproduct and a hydrogen-rich recycle gas; and

(4) recycling at least a substantial portion of said hydrogen-richrecycle gas to step (1).

2. A process as defined in claim 1 wherein said hydrofining catalystconsists essentially of a sulfided composite of nickel and molybdenumsupported on an activated alumina carrier.

3. A process as defined in claim 1 wherein said Group VIII noble metalis platinum or palladium.

4. A process as defined in claim 1 wherein said feedstock containsbetween about 5 and 500 p.p.m. by weight of organic sulfur.

5. A process as defined in claim 1 wherein said feedstock is a mineraloil fraction containing between about 5 and 300 p.p.m. by weight oforganic sulfide sulfur.

6. A process as defined in claim 1 wherein said feedstock is a mineraloil fraction containing heterocyclic sulfur compounds.

7. A process as defined in claim 1 wherein substantially the entireeffluent from step (1) is treated in step (2), without interveningseparation of hydrogen sulfide.

8. A process as defined in claim 1 wherein: said feedstock containsbetween about 5 and 500 p.p.m. of organic sulfur, at least a portion ofwhich is organic sulfide sulfur; said Group VIII noble metal is platinumor palladium;

the hydrofining conditions in step (1) are controlled to effecthydrodecomposition of at least about 80% of said organic sulfurcompounds; the hydrogenation conditions in step (2) are controlled toeffect hydrogenation of at least about 80% of the aromatic hydrocarbonsin said feedstock; and wherein said hydrogen-rich recycle gas in step(4) is scrubbed to remove H S prior to recycling to step (1).

9. A process for the hydrogenation of aromatic hydrocarbons in ahydrocarbon feedstock contaminated with organic sulfur compounds, whichcomprises:

(1) subjecting said feedstock plus added hydrogen to catalytichydrofining at an elevated temperature and pressure in contact with asulfactive hydrofining 8 catalyst comprising a Group VI-B metal orsulfide thereof, to effect hydro-decomposition of at least a portion ofsaid organic sulfur compounds with resultant production of hydrogensulfide;

(2) subjecting effluent from step (1), comprising hydrogen, hydrogensulfide and hydrocarbon feedstock, to catalytic hydrogenation in contactwith a sulfur-sensitive catalyst comprising a Group VIII noble metalsupported on an adsorbent, refractory oxide carrier having a crackingactivity higher than that corresponding to a Cat-A index of 25, saidhydrogenation being carried out at a temperature correlated with thecracking activity of said carrier so as to effect hydrogenation ofaromatic hydrocarbons in said feedstock with less than about 5 percentreduction in average molecular weight of the feedstock by hydrocracking;

(3) separating effluent from step (2) into a hydrogenated hydrocarbonproduct and a hydrogen-rich recycle gas; and

(4) recycling at least a substantial portion of said hydrogen-richrecycle gas to step (1).

10. A process as defined in claim 9 wherein said hydrofining catalystconsists essentially of a sulfided composite of nickel and molybdenumsupported on an activated alumina carrier.

11. A process as defined in claim 9 wherein said Group VIII noble metalis platinum or palladium.

12. A process as defined in claim 9 wherein said feedstock containsbetween about 5 and 500 p.p.m. by weight of organic sulfur.

13. A process as defined in claim 9 wherein said feedstock is a mineraloil fraction containing between about 5 and 300 p.p.m. by weight oforganic sulfide sulfur.

14. A process as defined in claim 9 wherein said feedstock is a mineraloil fraction containing heterocyclic sulfur compounds.

15. A process as defined in claim 9 wherein substantially the entireeffluent from step (1) is treated in step (2), without interveningseparation of hydrogen sulfide.

16. A process as defined in claim 9 wherein: said feedstock containsbetween about 5 and 500 p.p.m. of organic sulfur, at least a portion ofwhich is organic sulfide sulfur; said Group VIII noble metal is platinumor palladium; the hydrofining conditions in step (1) are controlled toeffect hydrodecomposition of at least about of said organic sulfurcompounds; the hydrogenation conditions in step (2) are controlled toeffect hydrogenation of at least about 80% of the aromatic hydrocarbonsin said feedstock; and wherein said hydrogen-rich recycle gas in step(4) is scrubbed to remove H 8 prior to recycling to step (1).

References Cited UNITED STATES PATENTS 3,132,089 5/1964 Hass et al208-89 3,405,190 10/1968 'Logemann et a1 260-667 3,527,695 9/1970Lawrence et al. 208l43 DELBERT E. GANTZ, Primary Examiner G. E.'SCHMITKONS, Assistant Examiner U.S. Cl. X.R.

